It is known to investigate thin surface layers on objects with spectroscopic electromagnetic radiation. Typically a mathematical model of the system is proposed for the entire system, and is data obtained corresponding to change in polarization state in a beam of electromagnetic radiation caused to interact with the system. A regression procedure is then performed to modify the values of parameters in the mathematical model to bring calculated results into agreement with measured data.
In some cases, however, the state of a sample as obtained, or entered into analysis, is initially unknown and proposing a mathematical model therefore is not possible. For instance, it comprises a substrate which was subjected to previous processing, the specific nature of which is unknown. This can be the case, for instance, where articles are manufactured via deposition or removal of material, to or from, a process substrate.
With the invention disclosed in this Specification in mind, prior art of varying degrees of relevance was identified.
Known Patents are:                U.S. Pat. No. 4,770,895 to Hartley is disclosed as it describes a application of ellipsometry controlling growth of alloy films.        U.S. Pat. No. 5,091,320 to Aspnes is disclosed as it describes application of ellipsometry to controlling material growth.        U.S. Pat. No. 5,626,117 to Wielsch et al. is disclosed as it describes a method for determining characteristic values of transparent layers using ellipsometry.        U.S. Pat. No. 5,582,646 to Woollam et al., is disclosed as it describes a system for applying ellipsometry to investigate samples.        U.S. Pat. No. 5,929,995 to Johs is disclosed as it describes a system for use in directing beams in process chambers.        U.S. Pat. No. 6,573,999 to Yang is disclosed as it describes determining film thickness using light absorption of material underlying a film.        U.S. Pat. No. 4,934,788 to Southw 11 is disclosed as it describes deposition of coatings using rate control.        
Known articles are disclosed in a bibliography format, as they are referred to throughout the Specification by the identifying number.    1. “Optical Characterization of Continuous Compositional Gradients in Thin Films by Real Time Spectroscopic Ellipsometry”, S. Kim and R. W. Collins, Appl. Phys. Lett. 67 (1995), 3010.    2. “Growth of AlxGa1−xAs Parabolic Quantum Wells by Real-Time Feedback Control of Composition”, D. E. Aspnes, W. E. Quinn, M. C. Tamargo, M. A. A. Pudensi, S. A. Schwarz, M. J. S. P. Brasil, R. E. Nahory, and S. Gregory, Appl. Phys. Lett. 60 (1992), 1244.    3. “Real-time Control of the MBE Growth of InGaAs in InP”, J. A. Roth, D. B. Chow, G. L. Olson, P. D. Brewer, W. S. Williamson, and B. Johs, J. Crystal Growth 201/202 (1999), 31.    4. “Status of HgCdTe-MBE Technology for Producing Dual-Band Infrared Detectors”, R. D. Rajavel, P. D. Brewer, D. M. Jamba, J. E. Jensen, C. LeBeau, G. L. Olson, J. A. Roth, W. S. Williamson, J. W. Bangs, P. Goetz, J. L. Johnson, E. A. Patten, J. A. Wilson, J. Crystal Growth 214/215 (2000), 1100.    5. In Situ Multi-Wavelength Ellipsometric Control of Thickness and Composition for Bragg Reflection Structures”, C. Horzinger, B. Johs, P. Chow, D. Roich, G. Carpenter, D. Croswell, and J. Van Hove, Mat. Res. Soc. Symp. Proc. Vol. 406 (1996), 347.    6. “Closed-loop Control of Resonating Tunneling Diode Barrier Thickness Using In Situ Spectroscopic Ellipsometry”, J. A. Roth, W. S. Williamson, D. H. Chow, G. L. Olson, and B. Jobs, J. Vac. Sci. Technol. B 18 (2000), 1439.    7. “In situ Spectral Ellipsometry for Real-Time Measurement and Control”, W. M. Duncan and S. A. Henck, Appl. Surf. Sci. 63 (1993), 9.    8. “In Situ Ellipsometric Diagnosis of Multilayer Thin Film Deposition During Sputtering”, X. Gao, D. W. Glenn, and J. A. Woollam, Thin Solid Films 313-314 (1998), 511. G. E. Jellison Jr., Thin Solid Films 234 (1993), 416.    9. “Spectroscopic Ellipsometry Data Analysis: Measurement Versus Calculated Quantities”, G. E. Jellison Jr., Thin Solid Films 313-314 (1998), 511.    10. “Overview of Variable Angle Spectroscopic Ellipsometry (VASE), Part 1: Basic Theory and Typical Applications”, J. A. Woollam, B. Johs, C. M. Herzinger, J. Hilfiker, R. Synovicki, and C. L. Bungay, SPIE Critical Reviews Vol. CR72 (1999), 3.    11. “Minimal-data Approaches for Determining Outer-layer Dielectric Responses of Films From Kinetic Reflectometric and Ellipsometric Measurements”, D. E. Aspnes, J. Opt. Soc. Amer. A 10 (1993), 974.    12. “Optical Approaches to Determine Near-Surface Compositions During Epitaxy”, D. E. Aspnes, J. Vac. Sci. Technol. A 14 (1996), 960. F. K. Urban III and M. F. Tabet, J. Vac. Sci. Technol. A 11 (1993), 976.    13. “Virtual Interface Method for In Situ Ellipsometry to Films Grown on Unknown Substrates”, F. K. Urban III and M. F. Tabet, J. Vac. Sci. Technol. A 11 (1993), 976.
14. “Real Time Monitoring of the Growth of Transparent Thin Films by Spectroscopic Ellipsometry”, M. Kildemo and B. Drevillon, Rev. Sci. Instrum. Vol. 67, No. 5 (1996), 1957.    15. “Characterization of Quasi-Rugate Filters Using Ellipsometric Measurements”, A. V. Tikhonravov, M. K. Trubetskov, J. Hrdina, and J. Sobota, Thin Solid Films 277 (1996), 83.    16. “Approximation of Reflection Coefficients for Rapid Real-time Calculation of Inhomogeneous Films”, M. Kildemo, O. Hunderi, B. Drevillon, J. Opt. Soc. Am. A 14 (1997), 931.    17. “Real-time In Situ Ellipsometric Control of Antireflection Coatings for Semiconductor Laser Amplifiers Using SiOx”, I-Fan Wu, J. B. Dottellis, M. Dagenais, J. Vac. Sci. Technol. A 11 (1993), 2398.    18. “Real Time Control of Plasma Deposited Optical Filters by Multiwavelength Ellipsometry”, T. Heitz, A. Hofrichter, P. Bulkin, and B. Drevillon, J. Vac. Sci. Technol. A 18 (2000), 1303.    19. “Direct Numerical Inversion Method for kinetic Ellipsometry Data. 1. Presentation of the Method and Numerical Evaluation”, D. Kouznetsov, A. Hofirchter, and B Drevillon, Appl. Opt. 41 (2002) 4510.    20. “Recherches Sur La Propagation Des Ondes Electromagnetiques Sinusoidales Dans Les Milieuc Stratifies Application Aux Couches Minces”, F. Abeles, Ann. De Physique, 5 (1950) 596.    21. “Thin-Film Optical Filters”, H. A. Macleod, McGraw-Hill, New York N.Y., 1989, p. 40.    22. “Ellipsometry and Polarized Light”, R. M. A. Azzam and N. M. Bashara, North-Holland, Amsterdam, 1977.    23. “Numerical Recipes in C”, W. H. Press, B. P. Flannery, S. A. Teukolsky, and W. T. Vetterling, Cambridge University Press, Cambridge, 1988.    24. Model M2000X, J. A. Woollam Co., Inc., Lincoln, NE USA.    25. “Data Analysis for Spectroscopic Ellipsometry”, G. E. Jellison Jr., Thin Solid Films, 234, 1993, 416-422.    26. “In situ and Ex Situ Applications of Spectroscopic Ellipsometry”, J. A. Woollam, B. Johs, W. McGahan, P. Snyder, J. Hale, H. Yao, Mat. Res. Soc. Proc., Vol 324, 1994, p. 15.
Even in view of the known prior art, need remains for a method of characterizing the outermost material on an article manufactured by deposition or removal of material to or from its surface, which method requires no prior knowledge of the composition of the article.